1. Field of the Invention
The present invention relates to a substrate cleaning method of and a substrate cleaning apparatus for removing contaminants such as particles adhering to various types of substrates (hereinafter referred to simply as “the substrates”) such as semiconductor substrates, glass substrates for photomask, glass substrates for liquid crystal display, glass substrates for plasma display, substrates for FED (Field Emission Display), substrates for optical disc, substrates for magnetic disk, substrates for magneto-optical disk and so on.
2. Description of the Related Art
A manufacturing process of electronic components such as a semiconductor device and a liquid crystal device includes a step of forming micro-patterns by repeating processing such as film deposition and etching on the front surface of the substrate. If there are particles adhering to the back surface of the substrate, the particles cause defocusing at a photolithographic step and makes it difficult to form desirable micro-patterns. Further, the substrate whose back surface carries the particles may give rise to cross contamination.
Vacuum sucking of the back surface of the substrate is often performed for transportation of the substrate, in the process particles may adhere to the back surface of the substrate. For this reason, a great number of techniques for cleaning the back surface of the substrate have been proposed. For instance, the apparatus according to JP-A-2010-27816 supplies an ultrasonic processing liquid, which is obtained by applying ultrasonic waves to a processing liquid, to the back surface of the substrate, thereby realizing ultrasonic cleaning. In an effort to prevent transmission of ultrasonic waves to the front surface of the substrate and damage upon patterns formed in the front surface of the substrate during ultrasonic cleaning, this apparatus forms a liquid film on the front surface of the substrate, freezes the liquid film and accordingly reinforces the patterns.
The apparatus according to JP-A-2010-27816 above is a cleaning apparatus which utilizes the principle of transmitting ultrasonic vibrations to a cleaning liquid and consequently generating micron-size air bubbles (cavitation bubbles) in the cleaning liquid. As powerful flows are created in the cleaning liquid owing to movements such as growth and collapse of cavitation bubbles, the particles adhering to the front surface of the substrate are released from the front surface of the substrate and washed away together with the cleaning liquid, whereby the front surface of the substrate is cleaned.
Like JP-A-2010-27816, JP-A-2013-84667 aims at suppressing damage to patterns which are formed on the front surface of the substrate, and discloses a technique which contains the substrate inside a housing section, supply a deaerated processing liquid to inside the housing section and apply ultrasonic vibrations on the processing liquid to thereby entirely clean the principal surface and the back surface of the substrate. A reduction of the dissolved gas concentration in the processing liquid decreases the amount of cavitation bubbles which are generated and suppresses damage to the patterns of the substrate.
Further, as other substrate cleaning technique using an ultrasonic processing liquid, JP-A-2004-363453 discloses an apparatus which supplies an ultrasonic processing liquid, on which ultrasonic vibrations are applied, to the front surface of the substrate from a nozzle while rotating the substrate to thereby clean the substrate. This apparatus moves the nozzle in a predetermined direction while maintaining the angle of the axis line of the nozzle with respect to the front surface and a peripheral area of the substrate. This blows the ultrasonic processing liquid toward not only the front surface of the substrate but the peripheral area of the substrate as well, and achieves ultrasonic cleaning.
Known substrate drying techniques include the technique according to JP-A-2014-197571 which hydrophobize the front surface of the substrate to reduce the contact angle between patterns and a liquid which fills the areas between the patterns and decrease force which acts upon the patterns during cleaning of the substrate to thereby discourage collapse of the patterns.